Since the 3rd Generation Partnership Project Release 5 (3GPP R5), a Universal Mobile Telecommunication System (UMTS) core network is divided into three subsystems including a Circuit Switched (CS) domain, a Packet Switched (PS) domain and an Internet Protocol Multimedia Subsystem (IMS). The CS domain is used for providing users with connections of circuit switched services, the PS domain is used for providing users with connections of packet switched services, and the IMS is a subsystem superimposed over the existing PS domain in the 3GPP R5. The IMS employs the PS domain as a bearer channel for the transmission of the upper layer control signaling and media data, introduces a Session Initial Protocol (SIP) as a service control protocol and provides abundant multimedia services for users by separating the service control and the bearer control and utilizing the characteristics of the SIP, i.e., simply, extensible and convenient for media combination.
Primary function entities in the IMS include: a Call Session Control Function (CSCF), configured to perform a user registration control, a session control and so on; an Application Server (AS), configured to provide various service logical control; a Home Subscriber Server (HSS), configured to manage subscription data of a user in a centralized manner; and a Media Gate Control Function (MGCF)/IMS Media Gateway (IM-MGW), configured to enable the interworking with a circuit switched network. A user may connect to the IMS through a Proxy-CSCF (P-CSCF) in the visited network, then session control, service triggering control and service control interaction with an AS are performed by the serving-CSCF (S-CSCF) of the home network.
The IMS architecture defined by the 3GPP solves all the key operability problems required for providing multimedia services over an IP bearer, such as roam charging, Quality of Service (QoS) and security guarantee, and has been accepted universally in the industry. Both the 3GPP2 and the Telecommunications and Internet converged Services and Protocols for Advanced Networking (TISPAN) define IP multimedia network architectures and service systems based upon the 3GPP model. Also, the 3GPP has started researches on the interworking of Wireless Local Area Network (WLAN) access with 3GPP system (I-WLAN), Fixed Broadband IMS (FBI) access, and the all-IP network (AIPN) supporting multiple access technologies. A user may be enabled to connect to the IMS according to the subscription of the user though access networks of different access technologies via a single multi-mode terminal or various types of terminals, so as to obtain uniform multimedia services, including a Voice over IP (VoIP) service. The above researches may possibly be related to a service involving the CS domain and the IMS simultaneously.
Particularly, the 3GPP Release 7 approves a work item to research on the issue of service continuity between a CS call and an IP-borne VoIP service provided by the IMS, while the IMS may be accessed though the WLAN or other IP access networks, i.e., a work item of Voice Call Continuity (VCC), including a research on a method for supporting a domain transfer between the CS call and the VoIP service provided by the IMS, so that the VCC may be achieved to accommodate the demands of network and service developments. The VCC service is a representative of services involving the CS domain and the IMS simultaneously.
In the development of 3GPP VCC, there is proposed a static anchoring and IMS centralized control method for the domain transfer. The basic idea lies in that, in the IMS home domain, the VCC user is assigned with an AS as a Call Continuity Control Function (CCCF), and control signaling of all the correlated CS calls and IMS sessions of the VCC user are routed to the AS for anchoring. The CCCF controls the above communication connection between the VCC user and a corresponding opposite user in a Third-party Call Control (3PCC) mode and accomplishes the domain transfer in accordance with a request from the VCC user. In other words, the communication connection between the VCC user and the opposite user is divided into two segments on the AS. When the VCC user decides to perform the domain transfer, the VCC user initiates to establish a connection to the AS in a transfer-in network domain. After the establishment of the new connection, the AS controls a renegotiation on the connection to the opposite user, so as to make the opposite user continue the voice communication with the VCC user over the new connection. As illustrated in FIG. 1, a CCCF controls the replacement of the two connections with the VCC user.
FIG. 2A, FIG. 2B and FIG. 2C illustrate procedures for establishing signaling and bearer connection during a domain transfer procedure from the CS domain to the IMS and a subsequent domain transfer procedure from the IMS to the CS domain for a CS originating call in the prior art. By the procedure, problems confronted by an online charging (or referred as a real-time charging) mode and a prepay service applying the online charging mode during a processing of a service simultaneously involving the CS domain and the IMS, may be shown.
Particularly, FIG. 2A illustrates a procedure for establishing signaling and bearer connection for a CS domain originating call before performing a VCC domain transfer from the CS domain to the IMS. In this procedure, the CS originating call of a VCC user is routed to a CCCF of the home IMS of the user for anchoring, and a bearer connection including a segment of CS bearer and a segment of IP bearer, segmented by an IM-MGW, are established between the VCC user and the opposite user (in FIG. 2A, it is assumed that the opposite side is at the IMS, and if the opposite user is at the PSTN, the connection from the CCCF to the opposite side may further go through an MGCF) as following.
1. The VCC user initiates a call in the CS domain at a Visited Mobile Switching Center (VMSC) in which the VCC user currently registers.
2. The VMSC triggers an originating side intelligent service in accordance with the subscription data of the VCC user, and sends an Initial Detection Point (IDP) message toward a GSM Service Control Function (gsmSCF) responsible for originating side's routing controlling.
3. The gsmSCF responsible for originating side's routing controlling returns a virtual roaming number pointing to the VCC user's home IMS, i.e., an IP Multimedia Routing Number (IMRN), through a Connect message, and in accordance with the Connect message, the VMSC routes the CS originating call to the CCCF assigned for the VCC user through other network elements in the CS domain, a CS/IMS interworking gateway MGCF and IMS-related network elements, and with the MGCF performing a CS-IMS interworking and converting the CS call to an IMS session, finally establishes a CS-IMS interworking session (dependent upon the IMRN, there may be actually different processing in the IMS, but this is not the focus of the present invention; as illustrated in the flow chart in FIG. 2, the IMRN includes a Public Service Identity (PSI) pointing to the CCCF, and the IMS-related network elements include an Interrogating-CSCF (I-CSCF)).
4. The CCCF terminates the received session as a final called party, interacts with the HSS to obtain the S-CSCF assigned for the VCC user (not illustrated), and then in accordance with information carried in the received session establishment request, reinitiates another segment of the session to the original opposite user on behalf of the VCC user through the S-CSCF, and correlatively controls the establishment of the two segments of the session in a 3PCC (also referred to as Routing Back-to-Back User Agent, i.e., Routing B2BUA) way.
5. Finally, the CS-IMS interworking session from the VCC user to the CCCF of the VCC user's home IMS domain via the CS domain and the CS-IMS interworking gateway, and the session from the CCCF to the opposite user are established, and the CCCF correlatively controls the two segments of the session to establish the bearer connection including a segment of CS bearer and a segment of IP bearer, segmented by an IM-MGW.
FIG. 2A illustrates merely one of implementations for anchoring the initial CS originating call to the CCCF in the user's home IMS. Alternatively, the user may directly insert a prefix to a called number or use a specific number pointing to the user's home IMS as the called number in the originated call, and the VMSC controls routing in accordance with the prefix or the specific number. Meanwhile, the number or the IMRN as described above may directly point to the CCCF as illustrated in FIG. 2, or may point to another AS. If the number or the IMRN points to another AS, the AS interacts with the HSS to obtain the S-CSCF currently assigned for the user and reinitiates a session to the original opposite user on behalf of the served user in accordance with the information carried in the received session establishment request, and then the S-CSCF triggers the session to the CCCF in accordance with an initial Filtering Criterion (iFC) in the IMS subscription data of the user, and so on. These are not the focuses of the present invention, and will not be described hereinafter.
Moreover, FIG. 2A illustrates a procedure for anchoring the initial CS originating call to the user's CCCF in the prior art. In addition, a procedure for anchoring an initial CS terminating call to the user's CCCF is also proposed in the prior art. As an alternative, a Gateway Mobile Switching Center (GMSC) in a called user's home PLMN receives a call establishment request destined to the user, interacts with an Home Location Register (HLR) to obtain terminating side CAMEL subscription data of the user, triggers a terminating side intelligent service in accordance with the data, and interacts with a gsmSCF responsible for terminating side's routing controlling to obtain an IMRN pointing to the home IMS. The GMSC, a CS/IMS interworking gateway MGCF and IMS-related network elements route the CS-IMS interworking session to the CCCF assigned for the user for anchoring in accordance the above information. Subsequently, through various processing in the prior art, such as a domain selection, call interworking and CS call delivery, the call is delivered to the user's VCC terminal, then the CS-IMS interworking session between the VCC user and the CCCF in the VCC user's home IMS domain via the CS domain and the CS-IMS interworking gateway, and the CS-IMS interworking session between the CCCF and the opposite user via the IMS-related network elements, the CS-IMS interworking gateway MGCF and the CS domain are established, and the CCCF correlatively controls the two segments of session to establish the bearer connection including two segments of CS bearer and a segment of IP bearer, respectively segmented by the IM-MGW on the both sides. Similar, these are not the focuses of the present invention, and will be not described hereinafter.
With reference to FIG. 2B, after anchoring the initial CS originating call or terminating call to the CCCF, the user initiates a CS-to-IMS domain transfer as follows.
1. When determining to perform a domain transfer to the IMS, if no IMS registration has been performed, the terminal firstly accomplishes an IMS registration (not illustrated), and then initiates an IMS originating session establishment request to the CCCF carrying information of the initial session, where a CCCF PSI carried therein is used as a domain transfer indication for requesting the CCCF to perform an operation of domain transfer for the currently established CS domain call to the IMS.
2. The S-CSCF assigned for the user routes the session establishment request to the CCCF in accordance with an iFC in user's subscription data.
3. The CCCF executes an SIP session transfer procedure for replacing the CS access leg of the user with an IMS access leg, accomplishes a redirection of a media stream interaction through UPDATE or re-INVITE over the segment of session with the opposite end, thus an end-to-end IP bearer connection between the opposite user and the VCC user is established.
4. Upon successfully performing the transfer of the SIP session, the signaling and bearer connection corresponding to the CS access leg of the VCC user is released.
With reference to FIG. 2C, a procedure for establishing a signaling and bearer connection during a subsequent domain transfer back to the CS domain is as follows.
1. After determining that it is needed to perform a VCC domain transfer back to the CS domain, if no registration has been performed at the VMSC, the terminal firstly registers at the VMSC (perform CS domain Location Updating, not illustrated), and then initiates a CS originating call to the CCCF, with a CCCF PSI carried therein as a domain transfer indication for requesting the CCCF to execute an operation of domain transfer back to the CS domain. The CS originating call is routed to the CCCF via an MGCF and an I-CSCF or S-CSCF.
2. The CCCF performs an SIP session transfer procedure similar to that described above for replacing the IMS access leg of the user with the CS access leg.
3. After successfully performing the SIP session transfer for replacing the IMS access leg with the CS access leg, the signaling and bearer connecting corresponding to the IMS access leg of the VCC user is released.
It shall be noted that the subsequent VCC domain transfer from the IMS to the CS domain has been described as an example in the above descriptions, but actually, the procedure of initial domain transfer from the IMS to the CS domain is the same as the procedure of subsequent domain transfer back to the CS domain, in other words, a history of the domain transfer need not be learned for the control of the CCCF.
Furthermore, similar to the procedure of establishing the CS originating call as illustrated in FIG. 2A, there may be different alternatives for the VCC terminal to establish a new CS access leg between the VCC terminal and the CCCF, including: the terminal directly initiates a call to a specific number, IMRN, which points to the user's home IMS and is indicated as a domain transfer request; or, the terminal initiates a call to a specific number indicated as a domain transfer request, the VMSC where the terminal is located triggers an originating side intelligent service in accordance with user's subscription data, and interacts with a gsmSCF responsible for originating side's routing controlling to obtain the IMRN pointing to the home IMS; and the VMSC, other network elements in the CS domain, the CS/IMS interworking gateway MGCF and IMS-related network elements route the CS-IMS interworking session to the CCCF assigned for the user in accordance the above information. FIG. 2C illustrates merely one of the simplest and most efficient approaches. Similarly, these are not the focuses of the present invention, and will not be described hereinafter.
It may be seen that in such a solution of implementing the Voice Call Continuity, a great influence may be introduced on charging based upon a call connection: for an initial CS call with the VCC user as a calling or called user, since it needs to be routed to the user's home IMS, a call connection will be established through both the CS domain and the IMS before domain transfer, resulting in repetitive charging for this period of time; and for one communication with the opposite user, during the procedure of domain transfer, the user will initiate the establishment of a call connection with the CCCF alternately in the IMS and in the IMS plus the CS domain, which make it difficult to form a complete charging record. Furthermore, in accordance with the current charging criterion, the charging for several communications with short duration is usually different from the charging for one communication with a long duration even with the same total duration. Consequently, even without consideration of the repetitive charging during the domain transfer, it is difficult for the method of separate charging in the CS domain and the IMS to guarantee completeness and accuracy of the charging. Also, since differences may usually exist in the case of establishing a call connection in different network domains and in the case of the user being a calling or a called user, a more flexible charging criterion may be desirable for such a scenario where two network domains are used dynamically and flexibly to establish and maintain a call connection. Furthermore, in the solution for Voice Call Continuity, regardless of the VCC user previously being a calling or a called user to establish the initial communication with the opposite user, the call connection between the VCC user and the CCCF newly established during domain transfer is always established by the VCC user in an originating way. Therefore for guaranteeing completeness and accuracy of the charging, a correct call direction has to be confirmed firstly, and the charging will be performed in accordance with the correct call direction. Obviously from the above, during such processing of a service which involves simultaneously the CS domain and the IMS, in order to implement a correct charging, the whole charging procedure may be very complicated. Particularly, if the method for separate CS domain and the IMS charging is still adopted, an essential requirement for implementation of complete and accurate charging is that a charging correlation in the CS domain and the IMS parts shall be guaranteed, and furthermore, a corresponding processing performed on information of the two correlated parts shall be guaranteed in the charging.
Further, there also exists a real-time charging or online charging mode in current networks, and services which adopt this mode include a prepay service widely applied. A basic feature of the prepay service is that, there is no long term credit relationship between a user and a network, the user prepays some fees and the network performs an online credit control while providing a service, in other words, a real-time deduction of a required fee, and when the prepay fees are exhausted, the provision of the service for the user is terminated.
In the current CS domain, the prepay service is typically based upon the Customized Application of Mobile Network Enhanced Logic (CAMEL) architecture, a primary procedure of the CAMEL is as follows: when the user originates or terminates a CS call, as the gsmSSF, a VMSC where the user is currently located (in the case that the user originates the call) or a GMSC (in the case that the user terminates the call) triggers an intelligent service in accordance with user's CAMEL subscription data, and then the VMSC or the GMSC establishes a control connection with the gsmSCF which provides a prepay service logical control. The gsmSSF reports call related information, monitors the procedure of call establishment and call continuance in accordance with an instruction of the gsmSCF and granted communication duration, and reports corresponding Basic Call Status Model (BCSM) events and Appling Charging Reports during call establishment and the call continuance. The gsmSCF performs a real-time deduction in accordance with the reported information, and judges whether to allow the user to continue with the communication in accordance with a remaining unit, so as to perform the CS domain credit control. Corresponding to the specific implementations introduced as above, before the VMSC or the GMSC routes the call to the CCCF of the user's home IMS, the prepay service implemented based upon the CAMEL is invoked in accordance with the user's subscription data, and the corresponding gsmSCF performs a real-time unit deduction during the call, and in accordance with the remaining unit, judges whether to allow or instruct a control of releasing the call so as to perform the CS domain credit control.
In the IMS, since both the service and the charging criterion are more complicated, an Online Charging System (OCS) as illustrated in FIG. 3 is adopted, which considers comprehensively different aspects with respect to a bearer, a session, an event, etc. The prepay service in the IMS may be also implemented in the architecture, as illustrated in FIG. 3. The OCS of the IMS includes a Bearer Charging Function (BCF), an Event Charging Function (ECF), a Session Charging Function (SCF), a Rating Function (RF), and an Account Business Management Function (ABMF). Based upon the above functions, the following three charging modes may be provided, including:
Immediate Event Charging (IEC): upon receiving a corresponding request, the OCS granting units to an IMS network element is performed in a single operation that also includes the deduction of the corresponding monetary units from a user account;
Event Charging with Unit Reservation (ECUR): the event charging with unit reservation includes the process of requesting, reserving, releasing and returning unused units for events. The deduction of the corresponding monetary units then occurs upon conclusion of the ECUR transaction.
Session Charging with Unit Reservation (SCUR): the session charging with unit reservation is configured for a credit control in a session, including the process of requesting, reserving, releasing and returning unused units for sessions, and the deduction of the corresponding monetary units. During a SIP session there may be repeated execution of unit reservation and debit operations.
The IMS network element may choose to apply the above different modes according to a service or a policy of an operator. In a VCC service, since the charging is for a voice communication, the mode of SCUR is adopted. During processing a session related to a corresponding user, information corresponding to the user is reported to the OCS through a Credit Control Request respectively of Initial, Update and Termination, in particularly, which can be accomplished through an interaction of the AS or S-CSCF in the IMS network with the OCS.